Unloading means for air-compressors.



- No. 664,562. I Patented Dec. 25. I900.

G.-DE LAVA]. & e. P. ABORN. UNLOADING MEANS 'FOR AIR- CUMPBESSORS(Application filed kpr. 3, 1900. (No Model.)

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. PatentedDe. 25, I900. a. .DE LAVAL &. a. P. ABORN; UNLOADINGMEANS FORAIR'COMPRESSOBS.

(Application filedApr. 3, 1900.-

- 2 SheetsSheet 2.

(No Model.)

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UNITED STATES PATENT OFFICE.

GEORGE D LAVAL, OF CAMBRIDGE, AND GEORGE P. ABORN, OF BOSTON,-MASSACHUSETTS, ASSIGNORS TO THE GEORGE E. BLAKE MANUFACTUR- ING COMPANY,OE NEW YORK, N. Y.

UNLOADING MEANS FOR AIR-'COMPRESORS.

SPECIFICATION forming part of Letters Patent No. 664.562, dated December25, 1960.

Application filed April 3, 1900. $eria1 No. 11.281. (No model.)

To all whom it may concern:

Be it known that we, GEORGE DE LAVAL, a resident of Cambridge, Middlesexcounty, and GEORGE P. ABORN, a resident of Boston, Suffolk county, Stateof Massachusetts, citizens of the United States, have invented certainnew and useful Improvements in Unloading Means for Air-Compressors orthe Like, fully described in the following specification and theaccompanying drawings,forming a part of the same.

In the operation of single-stage air-compressors it is common to provideunloading means by which the further compression of air is stopped andthe load upon the compressor-piston relieved when the air in thereceiver, such as a tank or any pipe system, exceeds the pressuredesired, and provision for thus stoppingthe compression of air andrelieving the load upon the compressor-piston in case of any such excessof-pressure and resuming compression or reloading the piston when thereceiver-pressure is again reduced has been made in various ways, as byopening and closing a connection between the opposite nds of thecylinder, through which the air may circulate without compression,opening and closing a relief-valve to the atmosphere or to an auxiliaryreceiver and otherwise.

The object of the present invention is to provide a multiple-stageair-compressor with unloading means, so as to secure the properunloading of all the pistons when the receiverpressure exceeds thepressure desired, so that the unloading and loading of the piston orpistons of the lower-pressure cylinder or cylinders shall becontrolledby the unloading means for the high-pressu re cylinder in such a manneras to assure the proper action of the other cylinders in relation to thehighpressure cylinder. We secure the result desired by combining orconnecting the unload ing means for the high-pressure cylinder and forthe lower-pressure cylinder or cylinders, so that the action of thefinal-receiver pressure controls not only the unloading means for thehigh-pressure cylinder, but also in connection with the pressure fromthe lowerpressure or intermediate receiver or rec'eiv'= ers controls theunloading means for the lower-pressure cylinder or cylinders. We

may combine or connect the unloading means for the high and lowerpressure cylinders in different ways and secure the result desired; butin controlling the unloading means for the lower-pressure cylinder orcylinders we preferably apply the final-receiver pressure and thepressure from the intermediate or lower pressure receiver for anycylinder in opposition to each other and in such a manner that on theoperation of the unloading means for the high-pressure cylinder thisfinal-receiver pressure, opposed by the intermediate-receiverpres'sure,is immediately cut Ofi or reduced, so that theintermediate-receiver pressure operates the unloading means for thelow-pressure cylinder.

The invention, broadly considered, may be applied in connection withdifferent systems for automatically throwing ofi the load from thecompressor-pistons when the final-receiver pressure is in excess of thatdesired and throwing it on again when this receiverpressure falls to orbelow the normal amount; but we preferably employ a construction inwhich the action of the unloading means is to open passages of amplesize between the two ends of the compression-cylinders, through whichthe air may circulate freely without work being done until the fall ofpressure in the air-receiver operates through the unloading means toclose the passages for resuming compression. Various forms of devicesalso may be employed in the unloading means; but in connection with ourbroadinvention of applying unloading means to multiple-stageair-compressors we have made also certain improvements in unloadingdevices which form in themselves specific parts of the present inventionand are applicable generally in connection with compressors whethersingle or multiple stage.

The present invention is intended for use in connection with eithersteam or power driven air-com pressors where the work is intermittent orthe final pressure liable for other reasons to exceed the pressuredesired; but

when the invention is applied in connection with a steam-drivencompressor we preferably combine with it a steam-regulator so arrangedthat when the unloading means is brought into action to unload thecompressorpistons the steam-supply to the engine is cut off or reduced,preferably being nearly shut Off, so that only a sufficient amount ofsteam is admitted to keep the compressor-pistons in motion, and whencompression is resumed the proper supply of steam is again admitted.

As a full understanding of the invention can best be-given by a detaileddescription of a construction embodying the same, such a descriptionWlll now be given in connection with the accompanying drawings, showinga two-stage steam-driven compressor embodying the invention in itspreferred form as appl'ed in connection with unloading the pistons byconnecting the cylinder ends for the circulation of the air withoutcompression, and the features forming the invention will then bespecifically pointed out in the claims.

In the drawings, Figure l is a plan view of the compressor. Fig. 2 is anend elevation. Fig. 3 is a vertical section on the line 3 of understoodthat fluid-pressure may be applied to all or any number of thedischargevalves and controlled so as to form a part of the unloadingmeans, in accordance with the size and character of the compressor andthe resultdesired. It will be understood also that the position and formof the dischargevalves and delivery-passages may be varied widely andthat the suction-valves, which are not shown, may be of any suitableform.

The high-pressure steam-cylinder takes its steam through theinduction-pipe L, on which is placed the regulator, hereinafterdescribed, and this high-pressure cylinder G exhausts into receiver M,(indicated indotted lines,) from which the low-pressure cylinder D takesits steam through pipe N, all as usual in cross-compound steam-engines.

Referring now to the unloading means used in connection with the generalfeatures of the air-compressor above described, there is mounted at oneside of the high-pressure cylinder B acylinder or barrel 0, in whichmove two plungers b c, secured in fixed positions on a plunger-rod 14,with a third plunger 61 forminga valve mounted loosely on the rodl be-Lil Fig. 2. Figs. 4:, 5, and 6 are vertical sections on respectively thelines 4, 5, and 6 of Fig. 1.

Referring to said drawings, A is the lowpressure and B the high-pressurecylinder of the two-stage air-compressor, the pistons of which areactuated through rods 00 y from the pistons of high and low pressuresteam-cylinders G D, the engine shown being a crosscompoundsteam-engine, although it will be understood that this is immaterial inrespect to the present invention. The compressorcylinder A has thesuction-pipe E and delivcry-pipe F and through the latter delivers tothe intermediate receiver or intercooler G, from which the high-pressureair-cylinder B takes its suction through suction-pipe H, and thiscylinder delivers through pipe I to the final receiver or pipe system.The cylinders A B are shown as having top discharge-valves connectingthe cylinders with delivery-passages K, leading to delivery-pipes F I.

The discharge-valves a, of which one is shown in section in Fig. 3, areof a comtnon form, with cylindrical extensions forming pistons 10,moving in cylinders 11, so that fluid-pressure may be applied to thesepistons, tending to close the valves, in addition to the lightclosing-springs l2, and these pistons seat tightly against thescrew-plugs 13, forming the ends of the cylinders 11 when the valves areopen, so as to prevent air leaking past the pistons and to the back ofthe valves. All the discharge-valves of the-two cylinders A B to whichpressure is applied in connection with the unloading means are of thesame form, and the construction of each of the two cylinders in respectto these valves tween the plungers b c. The plunger-rod 1a is connectedby a yoke 15 to a lever 16, on which are suspended the weights w,whichexert downward pressure upon the rod 14 and determine thereceiver-pressures at which the unloading means will be operated tounload and load the cylinders. The plunger?) has a seat 1 at the bottomof the cylinder 0, upon which seat it rests in its normal position, andthe receiver-pressure is applied below the piston I) through pipe 17,connecting with the receiver or pipe system, (not shown,) and thereceiver-pressure from pipe 17 in the normal position of the parts whenthe compressor is working is admitted also through the central port 2 inthe hollow rod 14 and transverse ports 3 to a chamber 18, with whichconnect pipes 19 20, connecting with the tops of the cylinders 11 on thehigh-pressure cylinder B and through which the receiver-pressure isnormally applied to pistons 10 in a direction tending to close thedischarge-valves a. The receiver-pressure in chamber 18, acting upon theupper side of the valve 1, is balanced by the pressure on the under sideof plunger 0. The upper end of the valve OZ is larger than the lowerend, and the shoulder thus formed seats upon an internal shoulder in thechamber O, the valve thus being seated by the pres sure due to thedifference in diameter of the opposite ends of the valve. As abovestated, the'valve d is loose on the rod 1 L, so as to have a smallamount of play transversely to and longitudinally of the rod 14, so thatthe valve may seat independently of the plunger 1), and a proper seatingfor both the plunger and the valve is thus secured without regard towear or inaccuracy of fitting. The valve d has a marginal port 4:extending longitudinally of the valve and connecting through port 5 inthe cylinder-wall with a chamber 21, having a connection through pipe 22with the suction-chamber of the low-pressure cylinder A, the port 4being of such length that when the valve 01 is raised by the movement ofplunger 19 under an excess of receiver-pressure the chamber 18 isconnected through this port 4 with the port 5 and chamber 21, and thusthe pressure in the pipes 19 20 and back of the valves a of thehigh-pressure cylinder is reduced to the suction-pressure of thecylinderA or the atmosphere. From the pipe 20, which normally containsair under receiverpressure from pipe 17 through the connections justdescribed, pipe 23 extends across the space between the two cylinders AB and connects with the top of a cylinder P, mounted at the side of thelow-pressure cylinder A, and there acts upon the top of a plunger e,forming a valve, the opposite or lowerend of which valve 6 is acted uponby pressure from the intermediate receiver G,admitted through pipe 24,connecting with the bottom of the cylinder P. This valve e also has aseat 1 upon which it rests in its normal position, as in the case of theplunger b of cylinder 0. Theintermediate-receiver pressure from pipe 24is also admitted through ports 6, extending through valve 2 to a chamber25, with which connect pipes 26, through which the pressure from theintermediate receiver is applied to the pistons on the discharge-valvesof the low-pressure cylinder A in the same manner as previouslydescribed in connection with the valves of the high-pressure cylinder Band shown in Fig. 3. The valve 6 also has the longitudinal marginal port7, which connects through port 8 with a chamber 27, which has aconnection with the suction-chamber of the cylinder A through pipe 28,and the port 7 of valve 6 is made of such length as to connect chamber25 with port 8 and chamber 27 when the valve 6 is forced upward by thepressure from the intermediate receiver through pipe 24 on the releaseof the final-receiver pressure on top of the valve 6, as hereinafterdescribed, so as to reduce the pressure on the backs of thedischargevalves of the low-pressure cylinder A to the suction-pressureof that cylinder or the atmosphere. A light spring 29 acts upon the topof the valve 6, tending to force it downward in addition to thefinal-receiver pressure from pipe 23, this spring acting to move andhold the valve down in its normal position when the excess of pressureon the lower side of the valve 6 is not sufficient to overcome thespring-pressure, thus assuring the proper normal position of the valvein starting the compressor.

The construction thus far described is complete as an unloading meansand may be used without a regulator for the steam-supply, even insteam-driven compressors, or any suitable form of regulator for thesteam-supply may be used with this unloading means, and it will beunderstood that thisunloading means may be used also with power-drivencompressors of various classes. In the case of steam-driven compressors,however, it is desirable that the steam-supply shall be cut OH or nearlycut off, so that just enough steam shall be admitted to overcome thefriction of the parts and keep the-engine running when thecompressor-cylinders are unloaded and that the proper supply of steamshall be ad- 7 33 of a balanced valve 34 in the valve-casing 35 on theadmission-pipe L, so as to tend to open the valve for the supply ofsteam to-the high-pressure cylinder C. Upon the valverod 33 acts also aspring 36, tending to close the valve, and the valve-rod 33 extendsoutside the cylinder 31 and carries on its screwthreaded end a stop 37,which is formed bya split nut adapted to be locked in any position bythe thumb-screw 9, so that it may be adjusted to the proper position onrod 33 to 5 secure just the desired admission of steam through valve 34when the receiver-pressure in cylinder 31 is relieved and the valvemoved toward its closed position by spring 36, the

amount of such closing movement being de- 10.

termined by the engagement of the stop 37 with the end of the cylinder31.

The operation of the unloading means and steam-regulator is as follows:All the parts are shown in the drawings as in their normal u 5 position,with the compressor-cylinders working and the full steam-supply admittedthrough valve 34. Assuming now that the pressure in the final receiverwith which pipe 17 connects reaches theexcessive pressure at which theunloading means is to be called into operation to unload the cylinders,the first elfect of this excessive pressure acting through pipe 17 uponthe bottom of the plunger bis to raise this plunger and rod.l4 against 115 the resistance of weights to on lever 16, carrying with it theplunger 0 and valve d. As the plunger b leaves its seat 1 at. the bottomof the cylinder 0 the area of the surface of the plunger 1) upon whichthe receiver-pressure from pipe 17 acts is immediately increased, thusincreasing the eifective pressure upon the piston 19 in such a mannerthat with a gradual start the speed is rapidly increased upon theplunger leaving it-s seat and exposing its full surface to theair-pressure beneath, and thus a rapid movement of the valve dis securedimmediately upon the start of the valve. This increase of pressure afterstarting the plunger Z) acts also to overcome the increase in theeffectof the weights to due to the change in angularity of theweightlever 16 as the lever is moved upward by the rod 14. This rapidupward movement of the In this construction the pipe 19, 8o

reduction of the pressure in chamber 18 andpipes 19 20 also the pressurein the top of the cylinder P is instantaneously reduced to thesuction-pressure of the low-pressure cylinder Aand the piston c incylinderP immediately moves up under the excess of pressure from theintermediate receiver through ,pipe 24, acting upon the bottom of thevalve 6, and as this valve 6 leaves its seat 1 an increased pressure andrapid movement of the valve is secured, as in the. case of the plungerb, so that the port 6 is at once closed to chamber 25, theintermediate-receiver pressure out off, and the chamber 25 connectedthrough ports 7 8 with the chamber 27, and thus through pipe 28 with thesuction of cylinder VA, so that the pressure upon the pistons on thebacks of the discharge-valves of the lowpressure cylinder A is thusreduced to the suction-pressure of that cylinder. The pressure upon thedischarge-valves of both cylinders A B, tending to hold them closed,being thus'relieved, these valves remain open by reason of the greaterpressure on the cylinder side, and-the air in each of thecompressorcylinders A B is thus circulated back and forth through'thepassages K from one end of each cylinder to the other without any workbeing done. The load being thus removed from both pistons of thecompressor, the compressor runs without doing work until a drop in thefinalreceiver pressure allows the Weightsw to move the rod 14 with itspistons in the regular operation of the compressor;

The receiver-pressure is thus again admitted from pipe 20 through pipe23 to the top of the cylinder P above the valve e, and the valve e isthus moved downward so as to again close chamber 25 to port 8 andconnect it through port 6 with pipe 24, and thus admit theintermediate-receiver pressure through chamber 25 and pipe 26 to theback of the dischargevalves of the low-pressure cylinder A, and thus thenormal operation of the low-pressure cylinder A is resumed. When thepressure in pipes 20 is reduced to the suction-pressure of cylinder A,as above described, the pressure in pipe 30, supplied through pipe 19,is

correspondingly reduced, and thus the pressure in cylinder 31, tendingto hold the valve 34 open, is relieved, so that the valve 34 is closedby spring 36 so far as permitted by the stop 37 ,and the supply of steamthrough valve 34 to the high-pressure cylinder B thus cut off or reducedto just the small amount desired to keep the engine running properly.When the receiver-pressure is again admitted to pipes-19 20 and thecylinders again loaded, as above described, the pressure in pipe 30 andcylinder 31 is correspondingly increased, and thus the pressure incylinder 31, acting upon piston 32, opens the valve 34 against thepressure of spring 36 to admit the proper supply of steam for thecompression-work.

While we have shown the unloading means as provided with piping throughwhich the unloading connection is made with the suction-chamber of thelow-pressure cylinder, it will. be understood that this connection maybe made directly to the atmosphere instead of through thesuction-chamber, as shown; but we prefer to make the connection to thesuction-chamber as shown, as the noise of an'open exhaust is thusavoided and the very objectionable feature of the delivery of dirt andoil which accompanies such openexhaust. In the case of compressors forelastic fluids other than air this becomes still more important.

It will be understood that while the especial object of the invention isto provide eflicient unloading means for multiple-stage aircompressors,and many features of the invention relate to such constructions, theunloading-cylinder constructions shown form in themselves parts of theinvention and may be used in connection with single-stageaircompressors. Thus if only a high-pressure cylinder B be used it isobvious that the crosspipe 23 will be omitted and the pipe 22 beconnected to the suction-chamber of cylinder B or be open to theatmosphere, and that the construction on the high-pressure cylinder Bthen forms a complete unloading means for a single-stage air-compressorcombined with a steam-regulator controlled by the unloading means. 7

In both multiple-stage and single-stage compressors it will be seen thata break in the final receiver or its connections will immediately resultin relieving the pressure on the backs of the discharge valves of bothcylinders, so that both pistons will at once be unloaded, and a break inthe intermediate receiver or'its connections will at once result inunloading the low-pressure piston. In the two-stage compressor shownalso it is evident that an excessive pressure in the intermediatereceiver, if such should exist from any cause, will result in moving theplunger e against the final-receiver pressure, so as to unload thepistons of the low-pressure cylinder.

An important specific feature of the unloading cylinder and plungerconstruction shown, although not essential, is the seating of theplungers at the lower ends of the cylinders, and thus reducing theeffective area of the plungers at the beginning of their movement, sothat the start is gradual; but the efiective area and speed rapidlyincrease upon the plungers leaving their seats, so as to secure a rapidopening by the valve of the connection between the pressure and exhaustchambers and overcome the increase in weight effect, which must resultfrom change in angularity of the weight-lever. A very sensitive andrapid action of the unloading devices is thus secured.

While the invention has been shown as applied to a two-stageair-compr'essor-that is, one in which only two cylinders are employeds0as to secure two compressions, it will be understood that the inventionis applicable generally in multiple-stage com pressors and that as manycylinders and compressors may be used as desired, the finalreceiverpressure and its release by the unloading means being applied inopposition to the pressure of the receiver to which each lower pressurecylinder delivers to control the unloading of such cylinder in the samemanner as shown and described in connection with cylinder A.

While the term air-compressor has been used throughout thisspecification and the term air applied to the fluid acted on, it will beunderstood that-these terms are intended to apply to compressors for anyelastic fluid other than air.

The broad invention of providing unloadin g devices for multiple stagecompressors may be applied in connection with unloading devices ofwidely-different forms from those shown and the desiredcontrol of theunloading of the lowerpressure pistons by the high and intermediatereceiver pressures may be secured in difierent ways, and the morespecific features of the invention are not to be limited to the exactform or arrangement of parts shown, but modifications may be madetherein by those skilled in the art without departing from theinvention.

What we claim is- T 1. In a multiple-stage compressor, the combinationwith cylinders operating at different pressures, of a valve controlledby the final pressure, and means controlled by the movement of saidvalve for unloading the pistons of the different cylinders,substantially as described.

2. In a multiple-stage compressor, the combination with a high-pressurecylinder and low-pressure cylinder, of a valve controlled by the finalpressure, and means controlled by the movement of said valve forunloading and loading the pistons of both cylinders including anunloading-valve for the low-pressure cylinder actuated by thereceiver-pressure of the low-pressure cylinder, substantially asdescribed.

3. In a multiple-stage compressor, the combination with a high-pressurecylinder and low-pressure cylinder, of a valve controlled by thefinal-receiver pressure, and means controlled by the movement of saidvalve for unloading the pistons of both cylinders including an nnloading-valve subjected to the finalreceiver pressure and theintermediate-receiver pressure tending to move the valve in oppositedirections and means for relieving said final-receiver pressure for themovement of said unloading-valve by the intermediatereceiver pressurewhen the pistons are to be unloaded, substantially as described.

4. In a multiple-stage compressor, the combination with a high-pressurecylinder and low-pressure cylinder, of a valve controlled by thefinal-receiver pressure, means controlled by the movement of said valvefor unloading and loading the piston of the highpressure cylinder, avalve subjected to the final-receiver pressure and theintermediatereceiver pressure tending to move the valve in oppositedirections, means controlled by said last-mentioned valve for unloadingand loading the low-pressure cylinder, and connections controlled by thefirst-mentioned valve forapplying the final-receiver pressure to saidlast-mentioned valve and relieving said pressure for unloading andloading the low-pressure piston when the high-pressure piston isunloaded and loaded, substantially as described.

5. In a multiple-stage compressor, the combination with thehigh-pressure cylinder and its unloading-valve controlled by thefinal-receiver pressure, of a low-pressure cylinder and anunloading-valve therefor the unloading movement of which is opposed bythe finalreceiver pressure, and means for applying and relieving thefinal-receiver pressure on the low-pressure unloading-valve by theunloading and loading movements of the highpressure unloading-valve forunloading and loading the low-pressure piston, substantially asdescribed.

6. In a multiple-stage compressor, the combination with a hi gh-pressurecylinder and its unloading-valve controlled by the final-receiverpressure, of a low-pressure cylinder and an unloading-valve therefor,connections controlled by the high-pressure unloadingvalve for applyingthe final-receiver pressure to the lowpressure unloading-valve, andconnections for applying the intermediate-receiver pressure to thelow-pressure unloading-valve in opposition to the final-receiverpressure, whereby the low-pressurennloading-valve is moved in onedirection for unloading by the intermediate-receiver pressure and in theopposite direction for loading by the final-receiver pressure and theaction of said low-pressure unloading-valve controlled by thehigh-pressure unloading-valve, substantially as described.

7. In a multiple-stage compressor, the combination with high and lowpressure cylinders having discharge-valves subjected to fluidpressuretending to close the valves and arranged torem-ain open for thecirculation of fluid'between opposite ends of the compressorcylijnderswhen said fluid-pressure is relieved, of a. valve controlled by thefinalreceiver pressure, and means controlled by the movement of saidvalve for applying and releasing the fiuid-pressu re on the backs of thedischarge-valves of both cylinders for loading and unloading thecylinder-pistons, substantially as described.

8. In a m ultiple-stage compressor, the combination with high and lowpressure cylinders having discharge-valves subjected to fluidpressuretending to close the valves and arranged to remain open for thecirculation of fluid between opposite ends of the compressorcylinderswhen said fluid-pressure is relieved, of a valve controlled by thefinal-receiver pressure, and means controlled by the movement of saidvalve for applying and releasing the fluid-pressure on the backs of thedischarge-valves of both cylinders for loading andunloading thecylinder-pistons, including an unloading-valve for the low-pressurecylinder actuated by the receiver-pressure of the low-pressure cylinder,substantially as described.

9. In a multiple-stage compressor, the combination with high and lowpressure cylinders having discharge-valves subjected to fluidpressuretending to close the valves and arranged to remain open for thecirculation of fluid between opposite ends of the com pressorcylinderswhen said fluid-pressure is relieved, of an unloading-valve for thehigh-pressure cylinder controlled by the final-receiver pressure, anunloading-valve for the low-pressure cylinder, connections controlled bythe highpressure unloading-valve tor applylng the final-receiverpressure to the loW-pressu re unloading-valve, connections for applyingthe dntermediate-receiver pressure to the lowpressure unloading-Valve inopposition to the final-receiver pressure, and means controlled by themovement of said valves for applying and releasing the fluid-pressure onthe backs of the discharge-valves of both cylinders for loading andunloading the cylinder-pistons, substantially as described.

10. In a multiple-stage compressor,the combination with a low-pressurecylinder, of unloading means therefor including an unloading-valvesubjected to a fluid-pressure tending to move the valve into its loadingposition and to the receiver-pressure of said cylinder tending to movethe valve into unload ing position, and means controlled by thefinal-receiver pressure for applying and relieving said fluid-pressurefor loading and unloading the piston of said cylinder, substantially asdescribed.

11. In a multiple-stage compressor,the combination with a low-pressurecylinder, of unloading means therefor including an unloadingvalvesubjected to the final receiver pressure tending to move the valve intoloading position and to the receiver-pressure of said cylinder tendingto move the valve into unloading position, and means controlled by thefinal-receiver pressure for applying and relieving said final-receiverpressure for loading and unloading the piston of said cylinder,substantially as described.

12. In a multiple-stage compressor, the combination with a low-pressurecylinder, of unloading means therefor includinga valve subjected onopposite sides to final receiver pressure and the receiver-pressure ofthe lowpressure cylinder tending to move the valve into its loading andunloading positions, and a spring acting on said valve with thefinalreceiver pressure, substantially as described.

13. In a multiple-stage compressor,the combination with the cylindersoperating at different pressures, of means for unloading the pistons ofthe different cylinders and controlling said unloading by the unloadingof the high-pressure piston, substantially as described.

14. In a multiple-stage compressor,the combination with the cylindersoperating at different pressures, of means for unloading and loading thepistons of the difierent cylinders and controlling said unloading andloading by the unloading and loading of the highpressure piston,substantially as described.

15. In compressor-unloading means,a fluidoperated plunger controllingthe unloading means and a seat therefor on which the plunger is normallyseated and by which the effective area of the plunger is reduced in itsnormal position and increased at the beginning of its movement,substantially as described.

16. ln compressor-unloading means,aflu1d operated plunger controllingthe unloading means and aseat therefor on which the plunger is normallyseated and by which the effective area of the plunger is reduced in itsnormal position and increased at the beginning of its movement, incombination with a weighted lever moved by said plunger, substantiallyas described.

17. In com pressor-unloading means,a fluidoperated plunger and a seattherefor by which I the effective area of the plunger is reduced in itsnormal position and increased at the beginning of its movement, and anunloadingvalve actuated by the plunger with lost motion between theplunger and valve at the beginning of the plunger movement,substantially as described.

18. The combination with cylinder 0, of plunger 1) having seat 1, pipe17 for admitting receiver pressure below said plunger and valve (1seated in the cylinder above plunger 6, substantially as described.

19. The combination with cylinder 0, of plunger 6 having seat 1, pipe 17for admitting receiver pressure below said plunger and valve (1 havingan enlarged head subjected to receiver-pressure and seated upon ashoulder in cylinder 0, with space between the plunger and valve,substantially as described.

20. The combination with cylinder 0 and pressure-chamber 18, of valve (1having a head subjected to the pressure in chamber 18 to seat the valve,plunger 0 on theopposite side of said chamber from the valve, andplunger 1) for actuating the valve with lost motion between the plungerand valve, substantially as described.

21. The combination with cylinder 0 and pressure and exhaust chambers18, 21, of plunger 5 and rod 14 having ports 2, 3, and valve (1 havingport 4 for connecting the pressure and exhaust chambers, substantiallyas described.

22. The combination with cylinder P, of valve 6 having seat 1 therein,unloading-ports controlled by said valve, pipe 24 for applyingintermediate-receiver pressure to said valve, and pipe 23 for applyingfluid-pressure in opposition to said intermediate-receiver pressure,substantially as described.

23. The combination with cylinder P, of valve 6, unloading-portscontrolled by said valve, pipe 24 for applying intermediate-receiverpressure to said valve, and pipe 23 connecting with the final receiverfor applying said final-receiver pressure in opposition to saidintermediate-receiver pressure, substantially as described.

24. The combination with cylinder P, of "alve e, unloading-portscontrolled by said valve, pipe 24 for applying intermediate-receiverpressure to said valve, pipe 23 connecting with the final receiver forapplying said final-receiver pressure in opposition to saidintermediate-receiverpressure, and spring 29 acting with thefinal-receiver pressure, substantially as described.

25. The combination with low and high pressure cylinders A, B, ofcylinders O, P, a high-pressure unloading-valve in cylinder 0 controlledby the final-receiver pressure, a low-pressure unloading-valve incylinder P, pipe 24 connecting cylinder P with the intermediatereceiver, and pipe 24 controlled by the high-pressure unloading-valvefor applying final-receiver pressure to said low-pressure valve inopposition to the intermediatereceiver pressure, substantially asdescribed.

In testimony whereof we have hereunto set our hands in the presence oftwo subscribing witnesses.

GEORGE DE LAVAL. GEORGE P. ABORN. Witnesses:

JOHN J. FINLEY, ALVAH F. DOLE.

